Cell Selection in a Cellular Communication System

ABSTRACT

A method in a user equipment for handling cell selection is provided. While in dedicated mode the user equipment receives from a radio network node a measurement information message which indicates at least two frequencies associated with a respective cell in a respective radio access technology. While it is in dedicated mode, the user equipment performs measurements on the frequencies to obtain a respective measurement value for each one of them, and receives a selection indicator message comprising a respective priority for each one of the frequencies. The user equipment obtains a respective threshold value for each of the frequencies and successively evaluates the frequencies in descending priority order until a frequency is determined for which the measurement value exceeds its respective threshold value. When entering idle mode, the user equipment selects cell based on the evaluation.

RELATED APPLICATIONS

This application claims priority to International Patent Applicationnumber PCT/SE2011/050182, which was filed Feb. 18, 2011 and isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments herein relate to a user equipment and a method in a userequipment. Embodiments herein further relate to a radio network node anda method in a radio network node. In particular, embodiments hereinrelate to handling cell selection.

BACKGROUND

In a typical cellular communication system, also referred to as awireless communication system, User Equipments (UEs) communicate via aRadio Access Network (RAN) to one or more core networks (CNs).

A user equipment may be a mobile terminal by which a subscriber canaccess services offered by an operator's core network.

The user equipments may be mobile stations or user equipment units suchas mobile telephones, also known as “cellular” telephones, and laptopswith wireless capability, and thus may be, for example, portable,pocket, hand-held, computer-included, or car-mounted mobile deviceswhich communicate voice and/or data with the radio access network.

Each cell in the cellular communication system covers a geographicalarea. A cell is served by Radio Base Station (RBS) equipment at a radiobase station site. That is, the radio base station provides radiocoverage in the cell and communicates over an air interface with userequipment units operating on radio frequencies within its range.

A radio base station is in some cellular communication systems alsocalled “eNB”, “eNodeB”, “NodeB” or “B node”, and will in this documentbe referred to as a Base Station (BS).

The part of the cellular communication system that handles thecommunications with the user equipments over radio link is referred tothe Radio Access Network.

Over the years, several different Radio Access Technologies (RATs) haveevolved, such as GSM, WCDMA and LTE.

Depending on the RAT in question, the RAN comprises different radionetwork nodes, which may be referred to by different names.

In GSM, the radio base stations are referred to as base stations, andare controlled by so called Base Station Controllers (BSCs).

In WCDMA, the base stations are controlled by so called Radio NetworkControllers (RNCs).

In LTE, the base stations are referred to as eNodeBs. There is no nodein LTE corresponding to the BSC or RNC units of GSM and WCDMA. In LTE,the base stations, eNodeBs, themselves comprise further functionalityand are interconnected to provide the required services in the RAN.

The different RATs may all exist in the same geographical area, andhence the user equipment may access the core network through differentRATs depending on, for example, which RAT provides the best coverage ata specific moment in time or at a specific location.

To enable coexistence of the RATs, the different RATs have their owncells, or frequencies, that are used for communication with the userequipments.

Cell selection, meaning that the user equipment selects a cell to campon, enables the user equipment to select another cell than the currentlyserving cell, for example if another cell in another RAT provides betterquality of service or coverage.

At times when the user equipment is not actively using the servicesprovided by the core network, it usually enters a so called “idle mode”.

In idle mode the user equipment continuously performs measurements onneighbour cells to enable cell selection using standardized idle modecell reselection algorithms. As input to the cell reselection algorithm,the user equipment uses system information which is broadcast in eachcell for all user equipments which are in idle mode and listening.

While in idle mode, the user equipment may indicate its presence to thenetwork by temporarily leaving idle mode to perform so called areaupdate procedures, either periodically or when the user equipmentchanges area. An area update may be referred to as a “Location Area”(LA) update, or “Tracking Area” update.

When the user equipment starts using the services of the core network,and for example gets involved in an activity such as a phone call, itleaves idle mode and enters into a so called “dedicated mode”.

When a user equipment is in dedicated mode, there are radio links,channels, set up between the user equipment and the RAN to enable thenecessary data transfer to provide the requested service. Such channelsmay be referred to as for example a Traffic Channel (TCH) and aStandalone Dedicated Control Channel (SDCCH).

When the call ends, a so called “channel release” message is signaledfrom the RAN to the user equipment to release the data transferchannels, whereupon the user equipment re-enters idle mode.

When the user equipment is in dedicated mode, it does not listen to thebroadcast system information, and does not perform cell selection.

When a call is released and the user equipment re-enters idle mode, itnormally selects the serving cell it had when the call was released, andperforms an area update if the area has changed during the call.

After the area update, the user equipment reads the broadcasted systeminformation and, if information about other RATs is provided in thesystem information, the user equipment may select a cell in another RATby using the measurements and broadcast system information as input toan idle mode cell reselection algorithm as mentioned above.

A move to another RAT may also be initiated at channel release by theRAN, by including a cell selection indicator in the channel releasemessage for the user equipment, indicating which frequencies/cells theuser equipment should select.

In order for the RAN to select a cell or frequency, to include in thechannel release message, in the same RAT as would be selected by theuser equipment idle mode cell reselection algorithm, the network mayneed to base the cell selection on user equipment measurements. Suchmeasurements need hence be sent in measurement reports from the userequipment while it is in dedicated mode, to the controlling radionetwork node in the RAN. Based on the measurements, the RAN may thendecide which cell provides the best radio connection for the userequipment, and direct it to a specific cell in a specific RAT.

The cellular communication system may also select RAT for the userequipment based on configuration.

A problem is that, during the actual cell reselection process and untilthe area registration is completed in the selected RAT, the userequipment cannot be reached from the cellular communication system. Thetime period during which the user equipment is unreachable due to thisis referred to as the “outage time”.

SUMMARY

In view of the discussion above, it is an object for embodiments hereinto provide an improved way of handling cell selection.

According to a first aspect, the object is achieved by a method in auser equipment for handling cell selection. The user equipment iscomprised in a cellular communication system. The user equipment entersdedicated mode. While it is in dedicated mode, the user equipmentreceives a measurement information message from a radio network node.The measurement information message indicates at least two frequencies.Each of the indicated frequencies is associated with a respective cellin a respective radio access technology. While it is in dedicated mode,the user equipment performs measurements on the indicated frequencies toobtain a respective measurement value for each one of the indicatedfrequencies. While it is in dedicated mode, the user equipment furtherreceives from the radio network node a selection indicator messagecomprising a respective priority for each one of the indicatedfrequencies. While it is in dedicated mode, the user equipment furtherobtains a respective threshold value for each of the respectiveindicated frequencies. The user equipment successively evaluates theindicated frequencies in descending priority order until an indicatedfrequency is determined for which the measurement value exceeds itsrespective threshold value. When entering idle mode, the user equipmentselects, based on the evaluation, the cell with which the determinedindicated frequency is associated.

According to a second aspect, the object is achieved by a user equipmentfor handling cell selection. The user equipment is comprised in acellular communication system. The user equipment comprises a receiverconfigured to, while the user equipment is in dedicated mode, receivefrom a radio network node a measurement information message indicatingat least two frequencies. Each of the indicated frequencies isassociated with a respective cell in a respective radio accesstechnology. The receiver is further configured to, while the userequipment is in dedicated mode, receive from the radio network node aselection indicator message comprising a respective priority for eachone of the indicated frequencies. The user equipment further comprises ameasurement unit configured to, while the user equipment is in dedicatedmode, perform measurements on the indicated frequencies to obtain arespective measurement value for each one of the indicated frequencies.The user equipment further comprises an obtaining unit configured to,while the user equipment is in dedicated mode, obtain a respectivethreshold value for each of the respective indicated frequencies. Theuser equipment also comprises an evaluation unit configured tosuccessively evaluate the indicated frequencies in descending priorityorder until an indicated frequency is determined for which themeasurement value exceeds its respective threshold value. Further, theuser equipment comprises a selection unit configured to when the userequipment enters idle mode, select, based on the evaluation, the cellwith which the determined indicated frequency is associated.

According to a third aspect the object is achieved by a method in aradio network node for assisting a user equipment in handling cellselection. The radio network node and the user equipment are comprisedin a cellular communication system. While the user equipment is indedicated mode, the radio network node signals to the user equipment ameasurement information message indicating at least two frequencies.Each of the indicated frequencies is associated with a respective cellin a respective radio access technology. While the user equipment is indedicated mode the radio network node further signals to the userequipment a selection indicator message comprising a respective priorityfor each one of the indicated frequencies.

According to a fourth aspect the object is achieved by a radio networknode for assisting a user equipment in handling cell selection. Theradio network node and the user equipment are comprised in a cellularcommunication system. The radio network node comprises a transmitterconfigured to signal to the user equipment when the user equipment is indedicated mode, a measurement information message indicating at leasttwo frequencies. Each of the indicated frequencies is associated with arespective cell in a respective radio access technology. The transmitteris further configured to signal to the user equipment while the userequipment is in dedicated mode, a selection indicator message comprisinga respective priority for each one of the indicated frequencies.

Thanks to embodiments herein wherein relevant measurements are performedby the user equipment, and wherein threshold values and priorities areobtained by the user equipment while it is still in dedicated mode, itis possible for the user equipment to select a cell which provides goodquality of service directly after reentering idle mode. Hence, theoutage time may be reduced.

Moreover, since the user equipment does not need to report measurementsof other RATs to the radio network nodes to enable evaluation and cellselection by the radio communication system, signaling load may also bereduced thanks to embodiments herein.

In addition, embodiments herein may provide a choice of more than oneRAT to select directly after a call release.

Other objects, advantages and novel features of embodiments herein willbecome apparent from the following detailed description when consideredin conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating an embodiment of acellular communication system.

FIG. 2 is a combined signalling scheme and flowchart illustratingsignalling in a cellular communication system.

FIG. 3 is a flowchart depicting embodiments of a method in a userequipment.

FIG. 4 is a schematic block diagram illustrating embodiments of a userequipment.

FIG. 5 is a flowchart depicting embodiments of a method in a radionetwork node.

FIG. 6 is a schematic block diagram illustrating embodiments of a radionetwork node.

DETAILED DESCRIPTION

Embodiments may be exemplified in the following non-limiting descriptionof embodiments.

FIG. 1 depicts a cellular communication system 100 in which embodimentsherein may be implemented.

The cellular communication system 100 comprises a first base station 105serving a first cell 110, a second base station 115 serving a secondcell 120, and a third base station 125, serving a third cell 130.

The first cell 110, second cell 120, and third cell 130 may belong todifferent Radio Access Technologies (RATs). In this example, the firstcell 110 belongs to a GSM-type RAT, the second cell 120 belongs to aWCDMA-type RAT, and the third cell 130 belongs to an LTE-type RAT.

The first base station 105 is controlled by a radio network node 135,which in this example is a BSC. The second base station 115 iscontrolled by a radio network node 140, which in this example is a RNC.The third base station 125 is in this example an eNodeB, and istherefore, as previously mentioned, not controlled by another radionetwork node in its RAN.

The radio communication system 100 further comprises a user equipment145, which in this example is a mobile phone.

In the example illustrated in FIG. 1, the situation is the following:The user equipment 145 enters dedicated mode at a first point in timet1, at which time the user equipment 145 is situated at a locationcorresponding to the beginning of arrow 146. The reason for the userequipment 145 entering dedicated mode may be for example that the userequipment 145 gets involved in a phone call.

While in dedicated mode, that is while the phone call is on-going inthis example, the user equipment 145 moves along a path corresponding tothe arrow 146.

At a second point in time t2, the phone call ends, and the userequipment 145 re-enters idle mode.

At the first point in time t1, that is when it enters dedicated mode asdescribed above, the user equipment 145 is served by the first cell 110belonging to the GSM-type RAT.

According to embodiments herein, the user equipment 145 receives, whileit in dedicated mode, from its serving base station, or from itscontrolling radio network node BSC 135, a measurement informationmessage. The measurement information message indicates at least twofrequencies. Each of the indicated frequencies is associated with arespective cell in a respective radio access technology.

In some embodiments, one or more of the indicated frequencies isassociated with more than one cell in the radio access technology.

In this example, the measurement information message indicates a firstfrequency corresponding to the first cell 110, which as previouslymentioned is a GSM-type cell. The measurement information messagefurther indicates a second frequency, corresponding to the second cell120 which, as also previously mentioned, is a WCDMA-type cell. In thisexample, the measurement information message also indicates a thirdfrequency, corresponding to the third cell 130 which is an LTE-typecell.

In other embodiments, more than one cell or frequencies for the same RATmay be indicated.

While the user equipment 145 is still in dedicated mode, it performsmeasurements on the indicated frequencies to obtain a respectivemeasurement value for each one of the indicated frequencies.

Hence, in this example the user equipment 145 performs measurements onthe first, second, and third indicated frequencies. The user equipmentthen obtains corresponding first, second and third measurement values.

Also while in dedicated mode, the user equipment 145 receives from theradio network node 135, a selection indicator message, comprising arespective priority for each one of the indicated frequencies.

The user equipment also obtains, still while in dedicated mode, arespective threshold value for each of the respective indicatedfrequencies.

The threshold values may be obtained from the radio network node 135, orfrom a memory unit in the user equipment itself, or from another radionetwork node.

To decide which cell to select, the user equipment 145 successivelyevaluates the indicated frequencies in descending priority order, untilan indicated frequency is determined for which the measurement valueexceeds its respective threshold value.

If sufficient information to perform the evaluation is obtained whilethe user equipment 145 is still in dedicated mode, the user equipment145 may in some embodiments perform the evaluation while it is indedicated mode. This may be the case for example if the selectionindicator message is received in relation to the measurement informationmessage which is received while the user equipment 145 is in dedicatedmode.

If the selection indicator message with the priority information and/orthe threshold values are received in a channel release message on theother hand, the evaluation may be performed when the user equipmentre-enters idle mode, since the channel release message is related to there-entry of the user equipment 145 to idle mode.

Based on the evaluation, the user equipment 145 may then when it entersidle mode, at time t2 in this example, select the cell with which thedetermined indicated frequency is associated.

In the example illustrated in FIG. 1, the third cell 130, which is ofLTE-type, has the highest priority. The second cell 120, which is ofWCDMA-type has the second highest priority, and the GSM-type first cell110 has the lowest priority.

Hence, in this example, the user equipment 145 will at the evaluationfirst evaluate if the third measurement value, corresponding to theindicated frequency for the LTE-type cell, exceeds its respectivethreshold value.

In this example the third measurement value does not exceed itrespective threshold value.

Therefore, the user equipment 145 will move on to evaluating the secondmeasurement value, which corresponds to the second cell 120 which hasthe second highest priority, and which in this example is a WCDMA-typecell.

In this example the second measurement value does exceed its respectivethreshold value. The user equipment 145 may hence not have to evaluatethe third radio measurement value, corresponding to the GSM-type cell,which in this example has the lowest priority.

Hence, when the user equipment 145 enters idle mode, it selects thesecond cell 120.

The described example may effectively reduce the outage time compared toknown methods where a user equipment first selects the current servingcell, that is the first cell 110 which is of GSM-type in this example,reads system information in the that cell, and then reselects the secondcell 130 which in this example is of WCDMA-type.

Moreover, compared to a case when the network may have redirected theuser equipment to another RAT, the user equipment 145 does not need tosend any measurement reports to the network for cell selection purposes.

To support mobility of user equipments between cells in the cellularcommunication system, so called handovers must be performed. Handoversare necessary for example when a user equipment, such as a mobiletelephone, leaves one cell and moves into another cell. Otherwise, forexample an ongoing call would be dropped, due to loss of radio coverage.

A handover may be a change of serving cell, so that a user equipmentbeing served by one cell, becomes served by another, so called candidatecell, instead.

A handover may also mean addition of a radio link to a candidate cellwithout removing established radio links to other cells; or replacementof one of the existing radio links by a radio link to a candidate cell.Communication that involves a multitude of cells may be referred to asmacro diversity, soft handover, softer handover or coordinatedmultipoint, etc.

It is naturally possible that the user equipment 145 illustrated in FIG.1 while it is in dedicated mode moves so far away from the cell 110which was serving it when it entered dedicated mode, that one or morehandovers to other so called candidate cells take place during the phonecall.

It is worth noting that in such situations, the measurement informationmessage and the selection indicator message may be provided by otherradio network nodes that are related to the candidate cells to which theuser equipment is handed over.

In some embodiments, the user equipment signals to the radio networknode an indication that it is capable of handling cell selection indedicated mode.

In case of handovers as described above, such an indication may beforwarded to a radio network node related to the candidate cell to whichthe user equipment is handed over.

In some embodiments more than one cell may be associated with one ormore of the indicated frequencies.

A measurement for each of the cells may then be performed, to obtain arespective measurement value for each of the cells associated with thefrequency.

Then, the evaluation may comprise comparing all the measurement valuesfor that frequency to the threshold value, to further evaluate if any ofthe measurement values exceed the threshold value, and also if so, whichone of the cells is the best choice for cell selection.

Embodiments herein, relating to methods for handling cell selection willnow further be described with reference to the combined signallingscheme and flowchart depicted in FIG. 2, which illustrates thesignalling in the example described above in relation to FIG. 1. Thesignalling illustrated in FIG. 2 takes place between the first point intime t1 and the second point in time t2 illustrated in FIG. 1.

That is, the signalling in FIG. 2 takes place when the user equipment145 is in dedicated mode.

The signalling in this example is the following:

Action 201

The radio network node 135 signals to the user equipment 145 ameasurement information message. The measurement information messageindicates at least two, and in this example three, frequencies. Each ofthe indicated frequencies is associated with a respective cell in arespective radio access technology.

Action 202

The radio network node 135 signals to the user equipment 145 a selectionindicator message. The selection indicator message comprises arespective priority for each one of the indicated frequencies.

In some embodiments, the selection indicator message further comprises arespective threshold value for each of the respective indicatedfrequencies.

Action 203

The radio network node 135 signals a channel release message. It is uponreceiving this message that the user equipment 145 re-enters idle mode.

Embodiments herein, relating to a method in the user equipment 145 forhandling cell selection, will now be described with reference to theflowchart depicted in FIG. 3. As previously mentioned, the userequipment 145 is comprised in a cellular communication system 100. Themethod comprises the following actions, which actions may be taken inany suitable order:

Action 301

The user equipment 145 enters dedicated mode.

Action 302

This is an optional action, according to which the user equipment 145may signal to a radio network node 105, 115, 125, 135, 140 an indicationthat the user equipment 145 supports handling of cell selection indedicated mode, that is, that is capable of cell selection as describedabove in relation to FIG. 1. The radio network node may be the firstbase station 105, the second base station 115, the third base station125, the BSC 135, the RNC 140, or any other suitable radio network node.

This may reduce the signalling, since the radio network node 105, 115,125, 135, 140 gets the information that the user equipment 145 mayitself select a cell when it re-enters idle mode. Thanks to thisinformation, the radio network node 105, 115, 125, 135, 140 does nothave to request reporting of radio measurements that it would haveneeded if it was to perform the cell selection for the user equipment145.

Action 303

While in dedicated mode, the user equipment 145 receives from the radionetwork node 105, 115, 125, 135, 140 a measurement information messageindicating at least two frequencies. Each of the indicated frequenciesis associated with a respective cell 110, 120, 130 in a respective radioaccess technology.

The radio access technologies may for example be GSM, WCDMA, or LTE.

In some embodiments, one or more of the indicated frequencies isassociated with one or more cells in the radio access technologyassociated with that frequency.

Action 304

While in dedicated mode, the user equipment 145 performs measurements onthe indicated frequencies to obtain a respective measurement value foreach one of the indicated frequencies.

In embodiments where one or more indicated frequencies are associatedwith more than one cell, as mentioned above, measurements may beperformed to receive a measurement value for each of the cells on thesame frequency.

The measured quality may be for example signal strength or/and signalquality of the cell.

Action 305

While still in dedicated mode, the user equipment 145 receives from theradio network node 105, 115, 125, 135, 140 a selection indicator messagecomprising a respective priority for each one of the indicatedfrequencies.

In some embodiments, the selection indicator message may be received inthe measurement information message.

In some embodiments, the selection indicator message may be received ina channel release message.

Action 306

While in dedicated mode, the user equipment 145 obtains a respectivethreshold value for each of the respective indicated frequencies.

In some embodiments, the respective threshold values are obtained in theselection indicator message.

Action 307

The user equipment 145 successively evaluates the indicated frequenciesin descending priority order until an indicated frequency is determinedfor which the measurement value exceeds its respective threshold value.

In some embodiments the evaluation is performed while the user equipment145 is in dedicated mode. This may for example be the case if sufficientinformation to do the evaluation has been obtained by the user equipment145 while the user equipment 145 is in dedicated mode, for example ifthe selection indicator message is comprised in the measurementinformation message, as mentioned above.

In some embodiments evaluation is performed when the user equipment 145enters idle mode. This may for example be the case if the selectionindicator message is comprised in the channel release message, asmentioned above.

In some embodiments, if more than one cell is associated with one ormore indicated frequency, and measurement values are obtained for one ormore of the cells associated with the same indicated frequency, then theevaluation may comprise comparing the measurement values of each suchcell with the threshold value. If the evaluation shows that more thanone of the cells for the same frequency exceeds the threshold value,than the cell which provides the best quality or signal strength may bechosen.

Action 308

When entering idle mode, the user equipment 145 selects based on theevaluation 306 the cell 110, 120, 130 with which the determinedindicated frequency is associated.

As mentioned above, if more than one cell is associated with anindicated frequency, the cell which provides the best quality or signalstrength may be chosen.

To perform the actions above for handling cell selection, the userequipment 145 comprises an arrangement schematically depicted in FIG. 4.As mentioned above, the user equipment 145 is comprised in a cellularcommunication system 100. The term “configured to” used herein may alsobe referred to as “arranged to”.

The user equipment comprises a receiver 400 configured to, while theuser equipment 145 is in dedicated mode, receive from the radio networknode 105, 115, 125, 135, 140 a measurement information messageindicating at least two frequencies. Each of the indicated frequenciesis associated with a respective cell 110, 120, 130 in a respective radioaccess technology. In further, receive from the radio network node 105,115, 125, 135, 140 a selection indicator message comprising a respectivepriority for each one of the indicated frequencies.

In some embodiments the receiver 400 is further configured to receivethe selection indicator message in the measurement information message.

In some embodiments the receiver 400 is further configured to receivethe selection indicator message in a channel release message.

The user equipment 145 further comprises a measurement unit 410configured to while the user equipment 145 is in dedicated mode, performmeasurements on the indicated frequencies to obtain a respectivemeasurement value for each one of the indicated frequencies.

The user equipment further comprises an obtaining unit 420 configured toobtain while the user equipment is in dedicated mode, a respectivethreshold value for each of the respective indicated frequencies.

In some embodiments, the receiver 400 is the obtaining unit 410, forexample if the respective threshold values are obtained by beingreceived in relation to the selection indicator message.

The user equipment 145 further comprises an evaluation unit 430configured to successively evaluate the indicated frequencies indescending priority order until an indicated frequency is determined forwhich the measurement value exceeds its respective threshold value.

In some embodiments the evaluation unit 430 is further configured toperform the evaluation while the user equipment 145 is in dedicatedmode.

In some embodiments the evaluation unit 430 is further configured toperform the evaluation when the user equipment 145 enters idle mode.

The user equipment further comprises a selection unit 440 configured to,when the user equipment 145 enters idle mode, select based on theevaluation, the cell 110, 120, 130 with which the determined indicatedfrequency is associated.

In some embodiments, the user equipment 145 further comprises atransmitter 450 configured to signal to the radio network node 105, 115,125, 135, 140 an indication that the user equipment 145 supportshandling of cell selection in dedicated mode.

The embodiments of the user equipment 145 for handling cell selectionmay be implemented through one or more processors, such as a processor460 in the user equipment 145 depicted in FIG. 6, together with computerprogram code for performing the actions of embodiments herein.

The program code mentioned above may also be provided as a computerprogram product, for instance in the form of a data carrier carryingcomputer program code for performing the embodiments herein when beingloaded into the user equipment 145.

One such carrier may be in the form of a CD ROM disc. It is howeverfeasible with other data carriers such as a memory stick. The computerprogram code may furthermore be provided as pure program code on aserver and downloaded to the user equipment 145, e.g. remotely.

The user equipment 145 may further comprise a memory 470 comprising oneor more memory units. The memory 470 is arranged to be used to storedata such as for example the indicated frequencies, the measurementvalues, the priorities and the threshold values. It may further bearranged to store applications to perform the actions of the embodimentsherein when being executed in the user equipment 145.

Embodiments herein, relating to a method in a radio network node 105,115, 125, 135, 140, for assisting a user equipment 145 in handling cellselection in a cellular communication system 100 will now be describedwith reference to the flowchart depicted in FIG. 5. As previouslymentioned, the user equipment 145 and the radio network node 105, 115,125, 135, 140 are comprised in cellular communication system 100. Theradio network node may be the first base station 105, the second basestation 115, the third base station 125, the BSC 130, the RNC 140, orany other suitable radio network node.

The method comprises the following actions, which actions may be takenin any suitable order:

Action 501

This is an optional action according to which the radio network node105, 115, 125, 135, 140 may receive from the user equipment 145 anindication that the user equipment 145 supports handling of cellselection in dedicated mode.

In some embodiments, such an indication may be forwarded by the radionetwork node 105, 115, 125, 135, 140 to another radio network node 105,115, 125, 135, 140 to which the user equipment is handed over while theuser equipment 145 is in dedicated mode.

Action 502

The radio network node 105, 115, 125, 135, 140 signals, to the userequipment 145 while the user equipment 145 is in dedicated mode, ameasurement information message indicating at least two frequencies.Each of the indicated frequencies is associated with a respective cell110, 120, 130 in a respective radio access technology.

Action 503

The radio network node 105, 115, 125, 135, 140 signals to the userequipment 145 while the user equipment 145 is in dedicated mode, aselection indicator message comprising a respective priority for eachone of the indicated frequencies.

In some embodiments, the selection indicator message further comprises arespective threshold for each one of the indicated frequencies.

In some embodiments, the selection indicator message is signalled in themeasurement information message or in a channel release message.

To perform the actions above for assisting a user equipment 145 inhandling cell selection, the radio network node 105, 115, 125, 135, 140comprises an arrangement schematically depicted in FIG. 6. As mentionedabove, the radio network node 105, 115, 125, 135, 140 and the userequipment 145 is comprised in a cellular communication system 100. Theterm “configured to” used herein may also be referred to as “arrangedto”.

The radio network node 105, 115, 125, 135, 140 comprises a transmitter600 configured to signal to the user equipment 145 while the userequipment is in dedicated mode, a measurement information messageindicating at least two frequencies, each of which indicated frequenciesis associated with a respective cell 110, 120, 130 in a respective radioaccess technology.

The transmitter 600 is further configured signal to the user equipment145 while the user equipment 145 is in dedicated mode, a selectionindicator message comprising a respective priority for each one of theindicated frequencies.

In some embodiments the selection indicator message further comprises arespective threshold for each one of the indicated frequencies.

In some embodiments, the transmitter 600 is further configured to signalthe selection indicator message in the measurement information messageor in a channel release message.

In some embodiments, the radio network node further comprises a receiver610 configured to receive from the user equipment 145 an indication thatthe user equipment 145 supports handling of cell selection in dedicatedmode.

In some embodiments, such an indication may be forwarded by the radionetwork node 105, 115, 125, 135, 140 to another radio network node 105,115, 125, 135, 140, to which the user equipment is handed over while theuser equipment 145 is in dedicated mode.

The embodiments of the radio network node 105, 115, 125, 135, 140 forassisting a user equipment in handling cell selection may be implementedthrough one or more processors, such as a processor 620 in the radionetwork node 105, 115, 125, 135, 140 depicted in FIG. 6, together withcomputer program code for performing the actions of embodiments herein.

The program code mentioned above may also be provided as a computerprogram product, for instance in the form of a data carrier carryingcomputer program code for performing the embodiments herein when beingloaded into the radio network node 105, 115, 125, 135, 140.

One such carrier may be in the form of a CD ROM disc. It is howeverfeasible with other data carriers such as a memory stick. The computerprogram code may furthermore be provided as pure program code on aserver and downloaded to the radio network node 105, 115, 125, 135, 140,e.g. remotely.

The radio network node 105, 115, 125, 135, 140 may further comprise amemory 630 comprising one or more memory units. The memory 630 may bearranged to be used to store data such as for example the indicatedfrequencies, the priorities and/or the threshold values. It may furtherbe arranged to store applications to perform the actions of theembodiments herein when being executed in the radio network node 105,115, 125, 135, 140.

According to embodiments herein, outage time may be reduced, and theneed for user equipments to send measurement reports to enable cellselection may be eliminated.

The embodiments are not limited to the above-described embodiments.Various alternatives, modifications and equivalents may be used.

When using the word “comprise” or “comprising” it shall be interpretedas non-limiting, i.e. meaning “consist at least of”.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appending claims.

1. A method in a user equipment for handling cell selection in acellular communication system, the method comprising: entering dedicatedmode, while in dedicated mode, receiving from a radio network node ameasurement information message indicating at least two frequencies,each of which indicated frequencies is associated with a respective cellimplementing a respective radio access technology, while in dedicatedmode, performing measurements on the indicated frequencies to obtain arespective measurement value for each one of the indicated frequencies,while in dedicated mode, receiving from the radio network node aselection indicator message comprising a respective priority for eachone of the indicated frequencies, while in dedicated mode, obtaining arespective threshold value for each of the respective indicatedfrequencies, successively evaluating the indicated frequencies indescending priority order until an indicated frequency is determined forwhich the measurement value obtained for that frequency exceeds itsrespective threshold value, and when entering idle mode, selecting basedon the evaluation the cell with which the determined frequency isassociated.
 2. The method according to claim 1, wherein the respectivethreshold values are obtained from the selection indicator message. 3.The method according to claim 1, wherein the selection indicator messageis received in the measurement information message and wherein theevaluation is performed while the user equipment is in dedicated mode.4. The method according to claim 1, wherein the selection indicatormessage is received in a channel release message, and wherein theevaluation is performed when the user equipment enters idle mode.
 5. Themethod according to claim 1, further comprising signaling to the radionetwork node an indication that the user equipment supports handling ofcell selection in dedicated mode.
 6. A user equipment for handling cellselection in a cellular communication system, the user equipmentcomprising: a receiver configured to, while the user equipment is indedicated mode, receive from a radio network node a measurementinformation message indicating at least two frequencies, each of whichindicated frequencies is associated with a respective cell implementinga respective radio access technology, and receive from the radio networknode a selection indicator message comprising a respective priority foreach one of the indicated frequencies, a measurement unit configured to,while the user equipment is in dedicated mode, perform measurements onthe indicated frequencies to obtain a respective measurement value foreach one of the indicated frequencies, an obtaining unit configured to,while the user equipment is in dedicated mode, obtain a respectivethreshold value for each of the respective indicated frequencies, anevaluation unit configured to successively evaluate the indicatedfrequencies in descending priority order until an indicated frequency isdetermined for which the measurement value obtained for that frequencyexceeds its respective threshold value, and a selection unit configuredto, when the user equipment enters idle mode, select based on theevaluation the cell with which the determined frequency is associated.7. The user equipment according to claim 6, wherein the obtaining unitis the receiver and wherein the receiver is further configured to obtainthe respective threshold values in the selection indicator message. 8.The user equipment according to claim 6, wherein the receiver isconfigured to receive the selection indicator message in the measurementinformation message, and wherein the evaluation unit is configured toperform the evaluation while the user equipment is in dedicated mode. 9.The user equipment according to claim 6, wherein the receiver isconfigured to receive the selection indicator message in a channelrelease message, and wherein the evaluation unit is configured toperform the evaluation when the user equipment enters idle mode.
 10. Theuser equipment according to claim 6, further comprising a transmitterconfigured to signal to the radio network node an indication that theuser equipment supports handling of cell selection in dedicated mode.11. A method in a radio network node for assisting a user equipment inhandling cell selection, the radio network node and the user equipmentcomprised in a cellular communication system, the method comprising:while the user equipment is in dedicated mode, signaling to the userequipment a measurement information message indicating at least twofrequencies, each of which indicated frequencies is associated with arespective cell implementing a respective radio access technology, andwhile the user equipment is in dedicated mode, signaling to the userequipment a selection indicator message comprising a respective priorityfor each one of the indicated frequencies.
 12. The method according toclaim 11, wherein the selection indicator message further comprises arespective threshold for each one of the indicated frequencies.
 13. Themethod according to claim 11, wherein the selection indicator message issignaled in the measurement information message or in a channel releasemessage.
 14. The method according to claim 11, further comprisingreceiving from the user equipment an indication that the user equipmentsupports handling of cell selection in dedicated mode.
 15. A radionetwork node for assisting a user equipment in handling cell selection,the radio network node and the user equipment comprised in a cellularcommunication system, the radio network node comprising a transmitterconfigured to signal to the user equipment, while the user equipment isin dedicated mode: a measurement information message indicating at leasttwo frequencies, each of which indicated frequencies is associated witha respective cell implementing a respective radio access technology, anda selection indicator message comprising a respective priority for eachone of the indicated frequencies.
 16. The radio network node accordingto claim 15, wherein the selection indicator message further comprises arespective threshold for each one of the indicated frequencies.
 17. Theradio network node according to claim 15, wherein transmitter is furtherconfigured to signal the selection indicator message in the measurementinformation message or in a channel release message.
 18. The radionetwork node according to claim 15, further comprising a receiverconfigured to receive from the user equipment an indication that theuser equipment supports handling of cell selection in dedicated mode.